In personal care applications, consumers are increasingly demanding formulations that provide multiple benefits such as, but not limited to, unique sensory experience, enhanced moisturization, increased conditioning, improved delivery of active ingredients and compatibility. These molecules can provide many of the above benefits listed either by themselves or in certain cases can have synergistic effects with principal functioning agents resulting in increased efficacy or a reduction in the amount of the agent used. These molecules can provide these benefits either while in use and/or after rinsing which makes them unique and opens the possibility to be used in both “leave on” and “rinse off” products. Synthetic rheology modifier polymers can be employed to assist in achieving one or more of these properties.
Typical synthetic rheology modifier polymers are: alkali-soluble emulsion (“ASE”) polymers, hydrophobically modified alkali-soluble emulsion (“HASE”) polymers, hydrophobically modified ethoxylated urethane (“HEUR”) polymers, and hydrophobically modified nonionic polyol (“HNP”) polymers.
HASE and ASE polymers, see, for example those described in, U.S. Pat. No. 3,035,004, U.S. Pat. No. 5,292,843, U.S. Pat. No. 6,897,253, U.S. Pat. No. 7,288,616, U.S. Pat. No. 7,378,479, and US Patent Publication No. 2006/0270563, have each been widely used as rheology modifiers in aqueous systems. However, some HASE polymers have shown deficiencies with respect to thickening efficiency, such as undesirably high sensitivity to relatively small variations in pH, electrolyte concentration, and the amount of polymer used. The thickening efficiency of such polymers in aqueous media tends to be low at low polymer concentration, for example, less than about 1% by weight polymer, particularly at low pH, such as for example, pH of less than about 6, but tends to markedly increase at higher polymer concentrations and/or higher pH. This sensitivity can lead to undesirably large changes in rheological properties, such as very dramatically increased viscosity, with relatively small changes in pH or polymer concentration. The disproportionately large changes in properties can lead to difficulty in designing a composition that has and maintains a desired performance profile under anticipated conditions of use, as well as to difficulties in manufacturing and handling such compositions.
U.S. Pat. No. 7,217,752 to Schmucker-Castner et al discloses a stable, aqueous composition containing a substantially crosslinked alkali-swellable acrylate copolymer rheology modifier, a surfactant, an alkaline material, and various compounds therein, as for example substantially insoluble materials requiring suspension or stabilization, such as a silicone, an oily material, or a pearlescent material. Additionally, this invention also relates to the formation of a rheologically and phase stable cationic hair dye composition.
Cross-linked ASE polymers have also shown deficiencies with respect to thickening efficiency and thus may, particularly at low pH, require an undesirably large amount of polymer to provide the desired level of thickening, and, when used in an amount sufficient to provide the desired rheological properties, impart a cloudy, translucent, or opaque optical appearance to aqueous compositions. A cloudy, translucent, or opaque optical appearance may be undesirable in end uses in which aesthetic criteria are important such as, for example, in personal care formulations, such as shampoos and body washes. Furthermore, some HASE and ASE polymers typically exhibit a lower thickening efficiency and/or impart a cloudy, translucent or opaque optical appearance in the presence of salts and surfactants, which also limits the usefulness of such polymers in some aqueous systems, such as for example, personal care compositions.
A desirable property in a formulation is yield. Yield is the ability to suspend particles in the formulation. One way to enhance yield is by employing structured surfactants. Structured Surfactant Liquid exhibit a close packed network of Multi-Lamellar Vesicles (MLVs) which accounts for their unique properties such as high loading of oils and fragrances. They are used in the Personal Care market to make rinse-off formulations (e.g. body washes and shampoos).
U.S. Patent Application Publication No. US2003/0180246 A1 discloses structured surfactant compositions that comprise an anionic surfactant and an alkanolamide. U.S. Patent Application Publication No. US2003/0190302 A1 discloses structured surfactant compositions that comprise an anionic surfactant and a cationic surfactant. U.S. Patent Application Publication No. US2006/0135627-A1 discloses structured surfactant compositions that comprise an anionic surfactant and an amine oxide.
U.S. Patent Application Publication No. 2006/040837 A1 discloses an aqueous, low pH structured surfactant composition, contains, based on 100 parts by weight of the composition, from about 3 parts by weight to about 40 parts by weight of one or more anionic surfactants selected from anionic phosphate ester surfactants, anionic sulfonate surfactants, and anionic carboxylate surfactants, wherein the composition exhibits a pH of less than about 5, exhibits shear-thinning viscosity, and is capable of suspending water insoluble or partially water soluble components.
U.S. Pat. No. 6,150,312 discloses when there is sufficient surfactant to form micelles (i.e. the concentrations are above the critical micelle concentration or CMC), for example spherical, cylindrical (rod-like) or discoidal micelles may form. As the surfactant concentration increases, ordered phases such as lamellar phase, hexagonal phase or cubic phase may form. The lamellar phase, for example, consists of alternating surfactant bilayers and water layers. These layers may be planar and/or fold to form submicron spherical onion like structures called vesicles or liposomes or spherulites. The lamellar phase having an ordered structure. The hexagonal phase, on the other hand, consists of long cylindrical micelles arranged in a hexagonal lattice. In general, the microstructure of most personal care products consists of either spherical micelles, rod micelles, or a lamellar dispersion.
One problem with certain lamellar phase compositions is that they tend to lose their lamellar stability in colder temperatures (e.g., −18° C. to 7° C. (0 to 45° F.)). During a freeze thaw cycle some structured surfactant formulations phase separate when the bi-layers of the MLVs (multi-lamellar vesicles) become unstable either through changes in bilayer elasticity or solubility of the surfactants. Improved structured surfactant systems, for example, systems with improved freeze-thaw stability, are desired.
Personal care formulations are launched on a global scale, thus their resistance through Freeze-Thaw is an important parameter. The stability requirement for a personal care formulation depends on the geography in which it is to be bought and sold. Indeed, according to the country in which the formulation is to be used, it will have to resist to very different temperatures, humidity, etc. Formulations may need to travel by truck, train or ship across very different temperatures, from freezing to desert heat. Therefore an acceptable “shelf life” is determined for each composition. It represents the amount of time during which the formulation should remain stable across its normal storage and handling conditions. It is measured between the time the composition is produced and when it is used by the consumer. Generally, personal care formulations require a two year shelf life.